The efficient utilization of HF is important from both economic and process operability viewpoints. Techniques to effect the separation and recovery of HF from fluorocarbon process streams have been disclosed.
U.S. Pat. No. 2,478,362 dicloses the use of a continuous separation zone to separate an organic phase from HF and then recycling the latter to the reactor feed system.
U.S. Pat. No. 3,406,099 discloses an azeotropic system useful for separation of CF.sub.3 COCF.sub.3, HF or CCl.sub.2 FCClF.sub.2 from mixtures containing one or more of these materials.
U.S. Pat. No. 3,873,629 discloses a continuous process for separating mixtures of HF and ClCHF.sub.2 by countercurrent contact of a gaseous mixture of the two components with H.sub.2 SO.sub.4.
U.S. Pat. No. 3,947,558 discloses a process for the separation of HF from the reaction products generated by fluorinating a 1-3 carbon chlorinated hydrocarbon by first separating HCl, followed by cooling to form an HF-rich late and an HCl-free organic layer. This latter layer is mixed with a liquid 2 to 8 carbon glycol; after which an HF-enriched glycol layer is separated from the halocarbon layer. HF is recovered from the glycol by distillation.
U.S. Pat. No. 3,976,447 discloses the separation of HF from gaseous mixtures by treatment with dry particles of CaCl.sub.2, BaCl.sub.2, or SrCl.sub.2, after which the HF is desorbed.
U.S. Pat. No. 4,209,470 discloses a process for the separation of HF from its liquid mixtures with 1-chloro-1,1-difluoroethane by adding an auxiliary solvent to enhance the HF composition of a liquid inorganic phase in a separation zone. The HF is then separated from the inorganic phase by distillation.
EP 98,341 discloses a process for the separation of HF and 1-chloro-1,1-difluoroethane which does not require an auxiliary solvent even through the feed stream to the separation zone contains pentafluorobutane which the disclosure states should contribute to the mutual solubility of HF and 1-chloro-1,1-difluoroethane; and therefore, should hinder a phase separation process. The separation is done without the use of auxiliary solvents by avoiding contamination and exercising good temperature control.
The need to produce alternate fluorocarbons useful as refrigerants and blowing agents or as intermediates in the production of other fluorocarbons useful as refrigerants and blowing agents has spurred an interest in processes for the preparation of FC-123 and FC-124. These are useful themselves as blowing agents, refrigerants and intermediates in the preparation of 1,1,1,2-tetrafluoroethane (FC-134a), a highly useful fluorocarbon refrigerant.
One process for the preparation of FC-123 and FC-124, described in commonly assigned application Ser. No. 070,826, filed July 7, 1987, involves vapor phase hydrofluorination of halogenated alkenes with excess HF. This process produces a reaction mixture effluent consisting essentially of HF, FC-123, FC-124, tetrachloroethylene, HCl and minor (less than 5 mole percent) amounts of other halogenated products, such as 1,2,2-trichloro-1,1-difluoroethane (FC-122) and pentafluoroethane (FC-125). Removal of HCl and FC-125 can be easily accomplished by simple distillation, leaving a mixture consisting of hydrogen fluoride (HF), FC-123, FC-124, tetrachloroethylene, and minor (e.g., less than 5 mol percent) amounts of other halogenated products. One method for separating the reaction mixture, described in Applicants concurrently filled application Ser. No. 226,737, utilizes the formation of HF azeotropes with FC-123 and FC-124 under conditions of controlled HF/FC-123 ratios.
The instant invention provides an alternate route to separation of HF from FC-123 and FC-124 utilizing phase separation and distillation.